This problem is on my 2004 Holiday Rambler Imperial motorhome. I recently attempted to replace the 120V water heater switch with a replacement because the old one did not illuminate when it was on. Otherwise it worked as expected. I'm guessing I mis-wired the new switch when I installed it. When I rocked the switch after installing it there was a momentary dim of the 12V lighting in the kitchen area. I reinstalled the old 120V switch but it no longer worked, nor did the LP water heater switch. I checked fuses and breakers in the rear panel and was not able to find a problem. My fuse panel in the bedroom area has a 15A F5 for the water heater, which was good, and a single leg breaker for the Suburban water heater which was not thrown. After reading posts on this subject on the forum I ohmed all fuses in this panel and found no problems. I was not able to detect 12V at either the LP or 120V switch in the kitchen area. I did find the relay for the water heater behind the 50A panel (R4) and it had 120V at Breaker #4 and Relay #4 terminals. The relays are soldered to a Model 760 50 Amp Smart EMS Controller. It looks like I lost control (LP and 120V) to the water heater. Have I missed a fuse or other simple fix? Any help would be appreciated.

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Does the WH work on LP gas? That would indicate the control board is O.K. You can also go thru the checks in this document. I realize your set up is a bit different since the 120 v power is managed by the Smart EMS Controller. I think that's your step after the above, make sure the relay or control board didn't go bad in it. If you search online perhaps you'll find a troubleshooting manual for it.

Check to make sure there is not an inline fuse to the vicinity of the two switch, I seem to remember someone finding an inline fuse to that location.

Also, the 120 volt water heater switch is actually a 12 volt switch that controls a relay for the water heater circuit. On my Windsor there is a small separate electrical box mounted on the wall behind the main panel. On my coach there are actually 2 relays in the box,one for the water heater and the other is for the engine block heater. The water heater circuit going from the EMS 750 panel goes to this panel. If you flip the switch the relay closes and the circuit energizes the 120 volt circuit as long as the EMS system allows it. You might check this relay.

Thanks for the additional inputs. The MH batteries were disconnected when I locked it up Sunday afternoon so that should address the recommendation from BFlinn181 to disconnect power. I have a schematic for the water heater circuit and I don't see an inline fuse near the kitchen WH switches. I have located the EMS panel jacwjames mentions and the WH relay does not respond to switch inputs. This jives with the fact that I was not able to measure 12VDC at either the 120V or LP WH switch in the kitchen. The Monaco/Holiday Rambler schematic 38040954 Diagram, Water Heater Wiring, shows the fused 12V signal coming off the rear fuse panel through a couple of connectors to the WH switch as a green switch input power signal that when closed should provide 12V to the WH relay pin 85 to turn it on. I think that's my homework, to verify the presence (or lack of) of 12V at the switch. I can also just short the green and gray WH switch wires and look/listen for WH relay closure.

General question: if the WH relay is bad what's the next step? It's soldered to the SMART EMS board. Is the entire board replaced? I'm eeing them online at $150-$200 and up.

Thanks for all the inputs, I appreciate it. I will take another run at it when I get a chance and report back.

Thanks for the replies with all the good suggestions. I live in Melbourne FL and recently evacuated the area for hurricane Matthew. While hunkered down in a Lakeland RV park I had some time to look into this problem a little further. Turns out jacwjames was spot on with his suggestion to look for a local fuse. There is an undocumented 12VDC 5A fuse in the vicinity of the switches in a fuse holder screwed to the sink cabinetry. And it was blown. It apparently supplies 12VDC inputs to both LP and 120V water heater switches. I only had to take one cold shower.